A major problem in high voltage integrated circuit technology is to find a satisfactory solution for the problem of isolation of components and sub-circuit sections. A solution to this problem was found in U.S. Pat. No. 5,300,448 in which a lateral linear doping profile was formed in the silicon layer of a SOI device. A lateral linear doping profile, as disclosed by this patent, has a minimum doping value at one end of the lateral distance of a thin film of silicon and a maximum doping value at a second opposite end of the lateral distance of the thin layer of silicon. Moreover, the silicon layer was provided as a thin layer of silicon having a thickness of about 2000 to 3000 angstroms. This structure formed a SOI semiconductor device having a high breakdown voltage characteristic.
This basic structure may suffer from problems occurring from external electric fields, caused by moisture or other contaminants on the surface of the wafer, acting on the drift region. Moreover, the prior structure has a higher device on-resistance than necessary.